It has been desired in magnetic recording media for high density recording that the surface properties of the magnetic layer be highly improved to reduce spacing loss between the medium and a magnetic head. For this purpose, not only must the surface properties of the magnetic layer be improved by improving the manufacturing techniques of the magnetic layer, but also the surface properties of the support have to be improved. It has been tried to make the thickness of the magnetic layer thinner in order to reduce thickness loss because the recording wave length is less with increased recording density and, as a result, the surface properties of the magnetic layer are more affected by the surface properties of the support.
However, there are limitations, due to the following reasons, on improving the surface properties of the support used for a magnetic recording medium. That is, as the surface properties of the film used as a support for the magnetic layer become better, frictional resistance to travelling rolls increase, and , as a result, in winding a cast film, it meanders or is wrinkled. Further, the film or web cannot be uniformly wound, because frictional resistance between opposite surfaces of the wound film increase.
Various solutions have been proposed to overcome these inconsistent factors. For example, it is disclosed in Japanese Patent Application (OPI) No. 109,605/78 that a magnetic layer be coated on a support on which stilted fine particle of a thermoplastic resin have been provided and removed by dissolution with a solvent. However, according to this method, the characteristics necessary for a magnetic recording medium for high density recording cannot be attained.